Index Properties of Soil and Its Formation

Properties of Soil and It’s Definition.


Soil is the substance existing on the Earths surface that may be dug or ploughed. In simple terms soil is a substance existing on the Earths surface, which grows and develops plant life. Soil can be also termed as, the un-aggregated or un-cemented deposits of minerals or fragments covering large portion of Earths crust.

Formation and Properties of Soil 

The formation of soil takes place due to chemical decomposition of rocks or due to mechanical disintegration of rocks. When a rock surface gets exposed to atmosphere to a specific time it gets disintegrated or decomposes forming small fine particles of soil. It process can be termed as ‘Geological Cycle’ in which soil is considered as incidental material obtained due to this process and this process goes on continuously in the nature.

Index Properties of Soil 

Physical properties of soil which are useful to identify and differentiate soils from one another are known as ‘Index Properties of Soil’. There are mainly 3 types of Index properties of soil and are as follows :

  • Particle size distribution ( coarse grained soil )

Determination of percentage of various sizes of particles in given mass of soil is called as ‘Particle size distribution’.

  • Relative Density or Density Index ( coarse grained soil )

It indicate relative compactness of soil. It is one of the most important factor for coarse grained soil. It is defined as the ratio of difference between the void ratio of cohesionless soil in its loose state and void ratio in its natural state to difference between its void ratio in its loose and dense state.


∴ emax = Maximum void ratio ( loose state )

∴ emin = Minimum void ratio ( dense state )

∴ e = Natural void ratio of soil.

  • Consistency ( fine grained soil )

Consistency is the term used to indicate degree of firmness of fine grain soil. When water is added to fine grain soil it reduces the adhesion and further displaces soil grain and turn it into liquid form. If water is evaporated from such suspension the soil passes through various stages of consistency i.e liquid state, solid state, semi-solid state and plastic state.

Also Read : Bearing Capacity of Soil and Its Importance.

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